Averaging of spectra

Examples of the two scaling versions are given for the IR spectrum of iso-propylmyristate in Fig. 10.57. 

The Averaging function generates an average speetrum from a set of original spectra of the same type. 

Select the spectra either by dragging these from the browser on the selection window  

In the latter case you also have to speeify the path and the data block of the files. 

If the option Update Av. Spectrum is not marked, the calculated average spectrum will be saved as a work file Av.x. If you eheek the Update Av. Spectrum box, an additional field will be displayed in whieh you have to drag an existing spectrum file to which the average data should be added. Usin the latter version you can carry out the averaging proeedure by adding spectra step by step. 

---

To record a mass spectrum it is necessary to introduce a sample into the ion source of a mass spectrometer, to ionize sample molecules (to obtain positive or negative ions), to separate these ions according to their mass-to-charge ratio (m/z) and to record the quantity of ions of each m/z. A computer controls all the operations and helps to process the data. It makes it possible to get any format of a spectrum, to achieve subtraction or averaging of spectra, and to carry out a library search using spectral libraries. A principal scheme of a mass spectrometer is represented in Fig. 5.2. To resolve more complex tasks (e.g., direct analysis of a mixture) tandem mass spectrometry (see below and Chapter 3) may be applied. 

Mineral standards were hand crushed to -1/4 inch, then ground to a fine powder in a ball mill (alumina elements) or Bleuler Model 526/LFS678 puck mill. The resultant powder was aerodynamically classified in a Bahco Model 6000 micro particle classifier and the finest fraction ( 18 throttle) was collected. A size criterion of 90% or more by weight of particles 5 micron and smaller in diameter was used for the mineral standards. Sizes were verified by Coulter Counter. Duplicate 13 mm KBr pellets were prepared and the spectra were weight-scaled by techniques similar to those reported by Painter (3) and Elliot (4). With one exception, all the mineral standard spectra were averages of spectra from duplicate pellets. The one exception was the iron sulfate spectrum, which was obtained as the difference spectrum by subtracting the spectrum of HCl-washed weathered pyrite from that of the weathered pyrite. A weight correction was applied to the difference spectrum. 

Bow Tie Trees. An example of the use of the microbeam to investigate the contaminants in a bow tie tree in polyethylene insulation is presented in figure 7 which shows a) the spectrum from the center of the tree, b) the average of spectra from the insulation outside the tree and c) the difference spectrum. The latter clearly shows the presence of aluminum, possibly a shard from the manufacturing process, as well as excess sulphur, chlorine, potassium, calcium, copper and possibly iron. 

Figures 8.15 and 8.16 show number and volume aerosol distributions in clean maritime air measured by several investigators (Meszaros and Vissy 1974 Hoppel et al. 1989 Haaf and Jaenicke 1980 De Leeuw 1986) and a model marine aerosol size distribution. The distributions of Hoppel et al. (1989) and De Leeuw (1986) were obtained at windspeeds of less than 5 m s 1 in the subtropical and North Atlantic, respectively. The distribution of Meszaros and Vissy (1974) is an average of spectra obtained in the South Atlantic and Indian Oceans during periods when the average windspeed was 12 m s-1. It is difficult to determine the extent to which the differences in these size distributions are the result of differences in sampling location and meteorological conditions such as windspeed (which affects the concentrations of the larger particles), or to uncertainties inherent in the different measurement methods.

For this analysis we select the Martian emission spectrum between 500 and 800 cm because the 667 cm CO2 band is well isolated and nearly free of lines from other constituents. The Martian spectrum has been measured by the infrared spectrometer on Mariner 9 with a spectral resolution of 2.4 cm and a good signal-to-noise ratio. Random errors are not noticeable in the large average of spectra shown in Fig. 6.1.1. The set of emission spectra displayed in Fig. 6.1.2 have been calculated with different spectral resolutions for a pure CO2 atmosphere with a surface pressure of 7 mbar and a surface temperature of 275 K. A temperature profile similar to that deduced from the measured spectrum, shown in Fig. 6.1.1, served in the radiative transfer calculations. The computed high resolution emission spectrum has been convolved with (sin27r Av/27t Av) instrument fimctions... 

IR spectroscopy is an inherently faster method than NMR and an IR spectrum is a superposition of the spectra of the various conformations rather than an average of them When 1 2 dichloroethane is cooled below its freezing point the crystalline matenal gives an IR spectrum consistent with a single species that has a center of symmetry At room temperature the IR spec trum of liquid 1 2 dichloroethane retains the peaks present in the solid but includes new peaks as well Explain these observations... 

Finding the values of G allows the determination of the frequency-domain spectrum. The power-spectrum function, which may be closely approximated by a constant times the square of G f), is used to determine the amount of power in each frequency spectrum component. The function that results is a positive real quantity and has units of volts squared. From the power spectra, broadband noise may be attenuated so that primary spectral components may be identified. This attenuation is done by a digital process of ensemble averaging, which is a point-by-point average of a squared-spectra set. 

For kaolinite the sample permeability was very low and the solution was poorly removed. The spectra (Figure 3C) are consequently complex, containing peaks for inner and outer sphere complexes, CsCl precipitate from resMual solution (near 200 ppm) and a complex spinning sideband pattern. Spectral resolution is poorer, but at 70% RH for instance, inner sphere complexes resonate near 16 ppm and outer sphere complexes near 31 ppm. Dynamical averaging of the inner and outer sphere complexes occurs at 70% RH, and at 100% RH even the CsCl precipitate is dissolved in the water film and averaged. 

Figure 13.6 Carbon-13 NMR spectra of 1-pentanol, CH3CH2CH2CH2CH2OH. Spectrum (a) i a single run, showing the large amount of background noise. Spectrum lb) is an average of 200 runs.

The sampling of solution for activity measurement is carried out by filtration with 0.22 pm Millex filter (Millipore Co.) which is encapsuled and attached to a syringe for handy operation. The randomly selected filtrates are further passed through Amicon Centriflo membrane filter (CF-25) of 2 nm pore size. The activities measured for the filtrates from the two different pore sizes are observed to be identical within experimental error. Activities are measured by a liquid scintillation counter. For each sample solution, triplicate samplings and activity measurements are undertaken and the average of three values is used for calculation. Absorption spectra of experimental solutions are measured using a Beckman UV 5260 spectrophotometer for the analysis of oxidation states of dissolved Pu ions. 

---